I'm surprised no one in the U.K. has posted about this yet. One of the benefits of being subscribed to Trains Magazine, as you also get their online newsletter.
http://trn.trains.com/news/news-wire/2016/05/03-new-campaign-looks-to-replace-london-subway-ads-with-cat-photos?utm_source=SilverpopMailing&utm_medium=email&utm_campaign=TRN_News_160509_Final&utm_content=&spMailingID=25443444&spUserID=MTE2MDY5NzM3MzAxS0&spJobID=801414501&spReportId=ODAxNDE0NTAxS0
http://trn.trains.com/news/news-wire/2016/05/03-new-campaign-looks-to-replace-london-subway-ads-with-cat-photos?utm_source=SilverpopMailing&utm_medium=email&utm_campaign=TRN_News_160509_Final&utm_content=&spMailingID=25443444&spUserID=MTE2MDY5NzM3MzAxS0&spJobID=801414501&spReportId=ODAxNDE0NTAxS0